Performance Check and Sensitivity Verification for UHF PD Measurements on Power Transformers

For examination and diagnostics of the insulation quality of high voltage devices the measurement of partial discharge (PD) is accomplished. The conventional PD measurement according to IEC60270 is in some situations not sensitive enough because of the high interference level in field. The development of an unconventional measuring method using electromagnetic probes is presented. These probes are inserted in the transformer tank during full operation via an oil valve normally used for oil filling. Due to the shielding characteristics of the transformer tank external electromagnetic disturbances are minimized and enable measurements with high signal-to-noise ratio. New experiences made in measurements in laboratory and in field lead to modified UHF PD probes. The newly developed probes have to be tested on their mechanical and electrical properties. For the functional test of UHF probes the Performance Check is presented. Taking a further step from the Performance Check to a Sensitivity Check which may in future allow an approximation of the PD quantity comparable to the apparent charge is discussed.